1. Field of the Invention
The present invention relates to a cantilever unit in which a cantilever and a displacement amount detecting means for it are integrated into one unit to attain a reduction in size, and to an atomic force microscope (hereinafter referred to simply as "AFM") which uses such a cantilever unit to measure the three-dimensional surface configuration of a specimen in nanometer scale. Further, the present invention relates to a reproducing apparatus and an information processing apparatus utilizing such an AFM.
2. Related Background Art
An AFM detects an atomic force acting between a specimen and a probe brought close to the surface of the specimen, up to a position at a distance of 1 nm or less therefrom, on the basis of the flexibility amount (the displacement amount) of a cantilever (an elastic body) supporting the probe, and makes it possible to observe the three-dimensional surface configuration of the specimen at a resolution of 1 nm or less by scanning the specimen surface while controlling the distance between the specimen and the probe in such a manner as to maintain this atomic force constant (Binnig et al., "Phys. Rev. Lett." 56, 930 (1986)). Unlike a scanning tunneling microscope (hereinafter referred to simply as "STM"), the AFM does not require the specimen to be conductive, so that it allows observation in atomic or molecular order of the surface of insulating specimens, in particular, the surface of semiconductor resists, biopolymers or the like. Thus, the AFM is expected to find a wide range of application.
FIGS. 5 and 6 show conventional AFMs. Basically, an AFM is composed of a probe 111 opposed to the specimen surface, a cantilever 107 supporting the probe, a means for detecting the amount of displacement of the cantilever due to the atomic force acting between the specimen and the probe, and a means for three-dimensionally controlling the relative position of the specimen with respect to the probe.
In the conventional AFM shown in FIG. 5, the detection of cantilever displacement amount is effected by an optical lever method according to which a light beam is applied from behind the cantilever 107, obtaining the displacement amount from the shift amount of the position of the reflected-light spot. In the conventional AFM shown in FIG. 6, a tunnel-current method is adopted, according to which a conductive probe 602 is arranged behind the cantilever 107 at a position close to it, and position control is performed on the conductive probe 602 in such a manner that the tunnel current flowing between the cantilever 107 and the conductive probe 602 is maintained constant, obtaining the displacement amount of the cantilever from the position control amount.
However, the optical lever method, described above, requires an adjusting jig for causing the light beam to be applied to the back surface of the cantilever, an optical component such as a lens 502 or a mirror, and a position adjusting jig for a half-split photodiode 504. The tunnel current method requires a jig for adjusting the position of the conductive probe 602 with respect to the back surface of the cantilever. Thus, in both methods, the mechanical structure of the cantilever displacement amount detecting means has to be rather large and complicated. As a result, the mechanical structure of the displacement amount detecting means is subject to positional deviation due to disturbances such as floor vibration, acoustic vibration, or temperature drift, or to generation of resonance due to deterioration in rigidity, thus making it difficult for the detection of the cantilever displacement amount to be effected at a satisfactory level of resolution.